Improved tedss bridge



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IMPROV'IID TRUSS BRIDGE.

GEORGE P. HERTHRL, JR., OF ST. LOUIS7 MISSOURI.

Letters Patent No. 59,769, dated .November 20, 1866.

SPECIFICATION- T0 ALL WHOM .'IT MAY CONCERN:

Beit known that I, GEORGE P. HERTHEL, jr., of the city and county of St. Louis, State of Missouri, have invented a new and useful Truss Bridge, and I do hereby declare that the following is a full and exact description thereof The nature of this invention is in the peculiar arrangement and shaping of the parts of the bridge in such wise that the strains, which vary in intensity at the various points of the entire span or length, shall nevertheless exercise a constant or nearly constant effect upon the material of the structure; thus, therefore, the amount of strain in each material section of the points. of the length being equalized or nearly equalized, the material section of the main parts of thetruss will be constant or nearly'constant, thereby'permitting uniformity of material and patterns for castings, te. i Moreover, the nature of said invention is in the adaptation tothe shape of truss so determined of such material as is not only best capable by its nature of resisting, with economy of weight, the strain, but also in the adaptation thereto of such material as may be easily reproduced in the4 uniform shapes required by said form of truss; for instance, cast iron or cast steel.

. In the application of brittle material like calst iron or steel to the said form of truss, if the strain thereon be unduly taken, the material is unable to withstand the same, and breakage or injury results; the nature of my invention, therefore, includes such detail .arrangement of parts composed of brittle material as will ensure a proper transmitting and taking of 'strains therein and thereon.

The general object of this invention is to produce an economical structure in weight and cost by changing the height of truss in such wise as to allow an unchangeable or nearly unchangeablemetal section or material section, thereby permitting the use of economical material such as cast iron, and at the same time by using such comparatively brittle' material only under legitimate'strains such as. compression; and, moreover, allowing the application 'of uniform parts of such material as wrought'iron under legitimate-strain of tension ;V and generallyv to prevent any material from being subjected to transverse strains, which, in consideration of buckling or warping, cause uncertainty and unsafety.l D n To enableithose skilled in the arts vto make and use my improved truss bridge, I will describe its detail, construction, and the action of its parts, referring herein to the accompanying drawings, in which similar letters designate similar parts of saiddrawings Figure 1 isa front elevation. Figure 2 a top plan of said truss. Figure 3 is a detail sectional elevation, showing the method of joining the parts of upper chord and posts and braces. Figure 4 shows the joint at the lower chord of posts, braces, &c. Figures 5 and 6 are theoretical lines of strain in the chords of a truss referred to in a more special manner hereafter.

It is well -known that in constructing the ,parts of a bridge, it is usual to assume the weight thereof as well as the added load equally distributed over its entire span, and thereupon determining the strain so caused-'in each part, and therefrom again its material form and material section or area. Moreover, it is known that upon the premise of an equally distributed load the strain in the upper and low'erchords'of a truss, whose chords are .horizontal or parallel, follows, if represented graphically, for all pointsof the span, the parabolic.

curve in gure 5. And in the same mannerthe curve of strain in the sides or braces follows'the line in fi ure 6.

g Thus, therefore, the material section of the chords and braces should vary as do the ordinates of said curves respectively; but as it is manifestly .impossible to vary said material section thus, itis usual to follow said curves as nearly as practicable by circumscribed polygonal lines. It is also known that by lthe inversion of the foregoing law of strain, if the upper and lower chords of a truss were made to follow the parabolic line of fig. 5, the strain line would be straight -or very nearly so, and hence the necessary material section of each chord uniform. This has therefore been advantageously used in the English- Fox it Henderson truss, and in the late German bridges of V. Pauli. These bridges have`moreover the advantage of throwing none other than compression or tension strains in said chords; but as in all said structures the upper chords were made of wrought iron, and this material, owing to its tendency to buckle, needed stiening, the same have not fully taken advan tage of the parabolic form as set forth in the nature of my invention. In the full knowledge, therefore, ofthe improvements thus made, I have arranged my said bridge with a parabolic polygonal upper chord, which, by the action of 'the loads acting thereon, su'ers compression and as by said form of chord the material section may remain uniform, I have adapted cast iron, or some similar material, which,by casting in forms, Amay be quickly x and cheaply reproduced, to said upper chord; said adaptation being rendered 4still more advantageous because -of the excellent manner in which cast iron, cast steel, or similar granular material, resists'said strain-vof coml pression.

I therefore, in the design o f my said truss, draw the parabola indicated by the dotted line in figure 1 passingr through the upper chord, describe on said parabola the polygon of the a ies of the parts composing the upper chord, either making equal lengths of panels or making equal lengths of the parts AB, BG, CI), tc.

Having thus given the general design oi' my said structure,lI will now give its practical construction.

I construct the upper chord of a series of vcast pipes or bars, (which latter in small trusses may have a section like-lla) and such other parts as are hereinafter mentioned. Said pipes or bars, F, are properly ribbed to prevent bucklig, and'otherwise form a piece of equal strength throughout. At thcendsofthe truss said pipes or bars rest upon the end pieces, G. i

These end blocks, G, receive also the lower chord or Stringer H.

One of the two end blocks G is intended to rest directly upon a proper base plate of the, abutment or pier, and the otheris intended to rest on rollers, which are properly placed upon the abutment or pier, so that here motion parallel to the length of the truss is admissible and not unduly resisted. v'Ihus the effects of expansion and.'contraction of the material of the truss are in such wise compensated as to do no' manner of injury to said truss.

Thelbracing or siding between the upper and lower chords is composed of a series of vertical posts, I, and inclined (diagonally in the panels) brace rods or bars, K. These said parts are, in the manner yet to be fully described, 'connected withsaid chords.

The posts, I, are intended to and do'usually resist a compressive strain caused by the tendency of the lowir and-.upper chords to lengthen; said postsl may thereforeproperly be constructed of cast iron orvsteel); and if made of wrought iron, they must he properly ribbed and strengthened to prevent buckling up. Now, as owing to a non-action of one of the adjoining tension braces, K, a strain of tension may be thrown upon I, said posts are connected with the chords F and VI-I (and with the braces K) in such wise as to fully act under said strain, as will yet be specified underthe description of the joints X and Y.

The braceslK su'er tension; they may be properly made of wrought iron; they are arranged to be quickly v adjusted to the camber or arch of the truss as is described under the heading of the joint Y.

The lower chord or Stringer, I'I, is made of wrought iron, its action being in greatest part to resist the horizontal thrust of the upper chord, F. y v

Now I would here especiallyl state that certain of said parts F Gr H I K may be dispensed with, or combined in such manner that for instance the braces K act both as posts and braces, &c. but in whatever arrangement theparts thus called to act may be constructed, I claim that in these partsthe principles enunciated as forming thenature of this invention hold good, and that in accordance with said principles the construction of detailswill be as herein described.

As has been stated, the compression strain lodged in the upper chord is sustained in the cast pipes or bars, F; these receive and transmit said strain to other parts of said truss at certain joints X in the manner following: a is a central bolt rod, suitably arranged with screw nuts at each end; -said bolt a passes through proper eyes or holes in the upper ends of the braces, K; it will be seen that the arrangement of said braces K is symmetrical with reference to the centre line a: y of' F; thus all strains transmitted by braces to the bolt a will in nowise act to twist the pipe or bar, F. Again, said bolt a receives the-post I; it will usually be best to arrange the post I witha forked end, the two prongs being both bored through to receive the said bolt a; thus again the action of all strain transmitted through I to a is in nowise to cause a turning or twisting tendency.

I In order to form a proper bearing for F, a muif will be placed around the bolt a, (shown as 6,) or said bolt itself may be simply enlarged (provision then being had to make a prong of Irremovable); said muti` orkr sleeve b is simply cylindrical and takes against its ends the prongs of I and the eye ends of K.

Outside of all said parts proper washers maybe placed on a., and then the s'crew nuts -being placed thereon, the parts are firmly secured. As theA ends of F bearing on a or its sleeve are properly rounded to t nicely, and as the arrangement of all parts I and K is such as to cause no warping or twisting ofc orv any other part, all strain will be taken axially, and either in the direction of the fibre or in the direction perpendicular thereto; thus are transverse strains avoided. Moreover, owing to the loop ends of the prongs of a slight or even/a moderately large strain of tension may be transmitted to, or be otherwise caused to be taken by, the posts I, thus adding security to thezstructure in case of non-action of a brace, K. Again, owing to the circular bearing of all parts, F, I, and K, on a (or a and said -parts may properly adjust themselves, and slightly change their relative angles to each other, and still there will exist a proper central -distribution and transmission of tension and compression strains; and in all such adjusting motion there will be no cause for transverse strains, excepting such as may arise from friction resistances to said motion.A

Lastly, the joint of the pieces F through a (or ad: b) as set forth, permits great simplicity in the manufacture of the pieces F, as the -'ends of each and every such piece may be cast and bored alike.

The joint Y between the parts I and K and the lower chord is made by the bolt d, having its ends properly threaded to'receive screw nuts. Said bolt 0l passes through eye-holes 'in the lowerlprongs of the posts I, the

joint being here similar to the onewith the bolt Aa above. Either the bolt d is made of sufficient body or it is properly surrounded by a sleeve, e, so thatthe braces K may run through the same witliit destroying the strength of the bolt d. At the under side said braces K are secured by proper nuts c, and when it is needful,

an additional or check nut may be added. By means of said nut r: the brace K may b e properly adjusted in itsv bearing length.

Usually outside of said parts I and K the lower chord H passes around d. In order that the bolt @Z may not cut out oi' the lower chord material and weaken it, I havearranged said lower chords as a double stringer of the parts g and g, these passing one above and the other below the bolt d. In order, then, to retain d in its place, I'secure the lap plates each side of g and g1 and surrounding d. Said plates being usually riveted to g and g1.' -Moreover all joints in eitherV Stringer g or g may be here conveniently and economically made y good under said plates g2; by all of which thelower chord` is male light and strong.

Outside of all said parts av washer may be put on each side, and then by proper nuts the saine may be securely held.

The joint Zat each end of the trussbetweeli tlieupper and lower chord is, as has been stated, accomplished by interposingthe end pieces G; these pieces' have a bearing g, of a proper rounding convexity, to receive the -last piece F; The lower chords H pass into said pieces G, the parts y and gl between joined by lap pieces g3,

and there being between said pieces g3 an opening (mortise) to receive the keys, g4; thus the pull of the lower chords is all taken fairly in said keys; these again, in passing out of G, press against the top and bottom parts thereofg thus this pressure transmits the strain in said lower chord into the end pieces, G, from which it is again transmitted through the pivot bearing g to the upper chord. Said keys y* being made with inclined edges, by driving the same down the lower chord may be drawn'tighter, thereby causing the upper chord to change its curvature by increasing the lversed sine thereof, or the camber; if then the braces K are again drawn tight to a bearing by the nuts k, the entire truss will be in all its parts properly readjusted. Thus, therefore, to a certain extent, the camber of the truss may be reproduced or changed.

The upper chord as well as the lower one and the posts- I may be of wood, inA which case the general detail would be strictly similar.

Having thus fully described my invention, what I specially claim is- 1'. A trussed bridge or other structure having flexible joints throughout, when constructed substantially in the manner herein described.

2. In the construction of truss bridges and other structures forming the joints between the posts, braces, and chords thereof, or either of them,by interposing a rod or bolt in such joint whereto said posts, braces, and chords shall be so pivoted or otherwise loosely connected as to form a flexible or yielding joint, each part being independent in movement, all substantially in the manner and for the'purpose herein set forth.

The arrangement of the braces K for adjustment of the parts forming the panels7 in combination with the keys g4 for adjustment of the end parts, thus' by said combination permitting a change or reproduction of camber substantially as set forth.

4. The general combination of the-parts F with Gr, H, I, and K, substantially as and for the purpose set forth. Y p

In witness whereof I have hereunto set my hand this 1st day of August, 1866, in the presence of- Witnesses: A*

CEAS. H. BoYLn, S. M. RANnoLPH.

GEO. P. HERTHEL, JR. 

